1. Field of the Invention
The present invention relates to spectroscopy and more specifically, the present invention relates to a system and method for beneficially coupling a sample and an internally reflecting element (IRE) within an attenuated total internal reflection (ATR) microscope.
2. Description of Related Art
Attenuated total reflectance (ATR) is an optical interrogation technique often used in conjunction with infrared spectroscopy, which enables samples to be examined directly in a solid, liquid or a gas state. In particular, ATR capitalizes on total internal reflected light produced at the interface of a configured internally reflecting element (IRE) and a coupled sample plane. In operation, a beam of light (e.g., infrared) is passed through the IRE crystal in such a way that it reflects at least once off the internal surface in contact with the sample. This reflection forms an evanescent wave which extends into the sample, often up to about 2 microns, with the exact value being determined by the wavelength of light, the angle of incidence and the indices of refraction for the IRE crystal and the sample medium being interrogated. The reflected beam, which carries the spectral information of the sample, is thereafter interrogated for analysis via, for example, a linear or 2 dimensional array detector.
As generally alluded to above, the samples (e.g., in solid form) to be interrogated using ATR as the investigation technique can come in the form of many different shapes and sizes as the desired samples are often cut, dissected, and polished for molecular analysis. Such mechanical preparation thus often provides rough and often unorthodox shapes that nonetheless still require being efficiently optically coupled between a diamond, silicon, or Germanium (Ge) crystal and a configured stage mechanism that embodies the heart of the microscope system.
In particular, the utilized high index crystal material, which is transparent to the interrogating beam, also provides for a configured hard surface (e.g., a concave, convex, beveled, but often flat surface) to enable compressive forces to be applied to such a configured surface(s) and a mechanical mechanism that introduces the sample. Therefore, a pressure mechanism is required to compress the sample tightly against the desired crystal surface but since the sample geometry is never truly orthogonal to the beam axis, the actual compression pressure varies across the sample area that is being interrogated.
Accordingly, by providing uneven pressure (e.g., for imaging ATR applications) over the interrogated sample area can result in a variation in the return signal strength and thus can degrade the desired spectral information. In addition, because samples can vary in density and hardness, (e.g., a powder sample may provide good results when compressed as opposed to a harder material that maintains its shape under compression) providing efficient compressive coupling between the stage mechanism and the sample surface geometry is desired in order to also not affect the investigating signal strength.
Conventional stages that encounter such signal strength problems discussed above, in addition to other mechanically induced deleterious effects, include mechanical screws, levers, slides, and actuators that are designed to apply desired compressive forces on a given sample. However, such mechanisms are complex, require frequent maintenance, require tight tolerances, and often only apply forces only along a single directional axis. Accordingly, the present invention is directed to addressing the complexity, sample geometry, in addition to feedback issues associated with such mechanical-only mechanisms.